rs-file-open-hot — measured, still hint
Status
hint. Wall-clock JSONL: rs-file-open-hot.jsonl. Not corpus-triaged. The 2026-10-22 corpus verdict does not cover this slug.
Measurement
File::open plus a short read of one one-byte file, 2000 times, versus opening once. rustc 1.99.1, -C opt-level=3, linux x64, load 0.59. The earlier 2750× pair was rustc 1.94 (16.615 ms vs 0.006 ms).
| role | case | median_ms | ops | ratio |
|---|---|---|---|---|
| after | open_once | 0.00478 | 2000 | 1 |
| before | open_each_iter | 1.987266 | 2000 | 415.746 |
The bench reopens one one-byte file. A path that changes every iteration cannot be hoisted; the measured cost is the open and read. Default stays hint. This ratio is not a general speedup.
Unblock
Do not set the default to error from this file alone. A changing input, a cold path, or another ABI can erase the difference. Corpus triage is still required before any default change.